There is growing pressure to reduce carbon dioxide emissions from industrial processes. The steam methane reforming (SMR) process, which is used in the production of ammonia, hydrogen, methanol, syngas, etc., is one of the significant contributors to CO2 emissions. A large hydrogen production plant may produce up to 900,000 metric tons of carbon dioxide per year, thus it may be considered a significant source of carbon dioxide.
In Europe, Canada, and California, carbon dioxide reduction regulations are being phased in gradually. This means that greenhouse gas (GHG) legislation remains a key consideration in future projects. The current understanding on this issue is that new plants will have to plan for carbon dioxide capture but may not be required to install and operate such systems at the project on-stream date. Therefore, industry desires a flexible carbon dioxide capture ready design that may be implemented when needed.
Steam methane reformers have two primary sources of carbon dioxide with 50 to 65% produced at high pressure along with the synthesis gas as a by-product of the steam reforming and shift reactions. The remaining CO2 is generated by combustion of a fuel in the reformer furnace at about ambient pressure. For synthesis gas producing processes that include a methanator, CO2 from the high pressure synthesis gas stream is selectively removed with an acid gas removal system such as an MEA, aMDEA, Benfield, etc. so that the CO2 is captured from the process gas as part of the overall process.
A portion of the CO2 emissions can also be captured from steam methane reformer designed to produce high purity H2 product. An acid gas removal system may be installed to remove CO2 in the process gas upstream of the pressure swing adsorber (PSA) unit. The PSA is used to produce the H2 product stream and a by-product tail gas stream. This option can capture about 50 to 65% of the overall carbon emissions generated from the steam methane reformer. The advantage of having the acid gas removal system on the process gas stream is that it operates at high partial pressure of CO2 in the CO2 removal system and requires relatively low energy for CO2 stripping. In many cases, it is possible to utilize a significant portion of the waste heat remaining in the process gas stream cooling train without the need to import additional energy in the form of low pressure steam. The disadvantage of installing an acid gas removal system on the high pressure process side for CO2 removal is that it requires a major retrofit effort, significant down time, and is disruptive to the current plant operation.
Additional CO2 can be captured if the reformer furnace is retrofitted or designed with a post-combustion CO2 recovery system such as Fluor's Econamine FG PlusSM, or Mitsubishi's KM CDR Process®. These systems remove CO2 from the flue gas from the reformer furnace stack. The flue gas stream is at a much lower pressure than the process gas stream.
A facility with CO2 recovery in the flue gas would be able to capture about 90% of the overall CO2 emissions from the facility. This process, if applied as a retrofit, would have minimum impact on design or operation of the existing facility and would be a “bolt-on” technology.
However, CO2 removal from low pressure flue gas has significant energy requirements per unit of CO2 removed. High energy usage to remove CO2 typically requires additional steam import from an outside source or use of a portion of the high pressure export steam produced by the reformer facility for CO2 stripping. Both options result in significant efficiency penalties and additional operational costs.
Industry desires to produce hydrogen by steam-hydrocarbon reforming while capturing carbon dioxide thereby decreasing or eliminating carbon dioxide emissions.
Industry desires to capture CO2 from industrial processes for sequestration, enhanced oil recovery, or other uses.
Industry desires high purity CO2. Industry desires a CO2 purity in the CO2 product stream of at least 95 mole % on a dry basis.
Industry desires to reduce greenhouse gas emissions, particularly CO2 emissions.
Industry desires to capture CO2 from industrial processes using proven unit operations and equipment.
Industry desires energy efficient and cost-effective retrofit solutions for capturing CO2 from existing facilities.
Industry desires an energy efficient large-scale hydrogen production process with decreased carbon dioxide emissions compared to conventional processes.
These and other desires of industry are addressed by the present process.